A wide variety of fluidizing apparatus are used in the art to facilitate mixing of a gaseous and solid medium. The apparatus range in complexity from a single chamber reactor, such as that described in Sawyer U.S. Pat. No. 2,642,339, to multi-chamber reactors, such as those described in Avery U.S. Pat. No. 3,765,101 and Reeves et at. U.S. Pat. No. 3,793,444. In multi-chamber reactors, each chamber is usually separated from the next by a foraminous member, commonly known as a distributor plate or baffle, to prevent excessive channeling and bubbling of gas through the fluidized bed and to increase the length of the reaction zone beyond that which could be achieved without the use of such foraminous members. Various design concepts relative to the use of foraminous members for fluidized beds are known in the literature, e.g., A.I.Ch.E. Jour., Vol. 5, No. 1, March 1959, pp. 54- 60.
Many multi-chamber fluidizing aparatus described in the art employ distributor plates or baffles having conically shaped holes through which gas is passed to promote fluidization of solid particles contained in or fed to a reaction chamber above the plate or baffle. In such apparatus it is usually considered undesirable for any significant amount of solid particles to drop through the plate or baffle or build up on the surface thereof. As a consequence, the apparatus is often operated at high superficial gas velocities, e.g., 15 to 30 ft./sec., and the plate or baffle is commonly designed to have a pattern of sharp edges to minimize flat areas on the surface of the plate or baffle which is exposed to settling solid particles. When lower superficial gas velocities are employed, the plate or baffle is often equipped with a gaspermeable cap or plug to prevent backflow of solids.
For solids catalyzed reaction where high surface area is important, the use of high superficial gas velocities in fluidizing apparatus is economically unattractive because the resulting fluidized beds are so dilute that the amount of material reacted per unit of reactor volume is relatively small. In fluidizing apparatus employing lower superficial velocities, e.g., Sawyer U.S. Pat. No. 2,642,339, the fluidized bed is quite dense and it is not practical for the bed depth to exceed a certain maximum level without encountering excessive channeling and bubbling of gas through the bed. That maximum size is, moreover, well below the minimum size that is considered to be commercially attractive.
To overcome the low reaction efficiency of dilutephase high superficial velocity fluidizing systems and the size limitations of dense-phase fluidizing systems, the fluidization method described in Reeves et al. U.S. Pat. No. 3,793,444 employs a reaction vessel containing a plurality of reaction chambers, each separated by a foraminous member, through which the flow of gases and solid particles is recirculated to produce a flooded dense fluidized mass with pneumatic transport of solids throughout the reaction vessel. The pressure drop between successive reaction chambers is maintained in the range of 0.5 to 10 psig. In operation the low pressure drop across the foraminous member, which is flooded on both surfaces by a dense fluidized mass, can cause some of the openings in the foraminous member to plug resulting in less efficient operation. In addition, when the flooded dense bed is fluidized at high temperature, the combination of heat and fluid forces which is exerted on conventionally designed foraminous members can cause considerable warping in metal members and excessive cracking in ceramic members.
The invention provides for a foraminous member, especially designed for use in flooded multi-chamber fluidizing apparatus, which sustains the fluidization of a cocurrent continuous flow of gases and solids therethrough without plugging or cracking.